|Publication number||US7495742 B2|
|Application number||US 11/013,252|
|Publication date||Feb 24, 2009|
|Filing date||Dec 15, 2004|
|Priority date||Dec 15, 2003|
|Also published as||US20050128447|
|Publication number||013252, 11013252, US 7495742 B2, US 7495742B2, US-B2-7495742, US7495742 B2, US7495742B2|
|Original Assignee||Canon Kabushiki Kaisha|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (14), Referenced by (1), Classifications (11), Legal Events (3)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The present invention relates generally to a measuring method and apparatus, and more particularly to a measuring method and apparatus for measuring an optical performance, such as a wave front aberration and the best focus position, of a projection optical system for transferring a pattern on a mask onto an object, and an exposure method and apparatus that are corrected using the measuring method and apparatus. The inventive measuring method and apparatus are suitable, for example, for measurements of the projection optical system used for a step-and-scan exposure apparatus or a scanner. The step-and-scan exposure apparatus exposes a mask pattern onto a wafer by continuously scanning the wafer relative to the mask, and by moving, after one shot of exposure, the wafer stepwise to the next exposure area to be shot.
A projection exposure apparatus has conventionally been used to transfer a pattern on a mask or a reticle onto an object to be exposed in manufacturing semiconductor devices in the photolithography process. A type of the exposure apparatus is shifted from the step-and-repeat exposure apparatus (“stepper”) to the scanner. The exposure apparatus is required to transfer a pattern on the reticle onto the object at a predetermined magnification with precision, and exposure at the best focus position using a projection optical system having a reduced aberration is important. In particular, due to the recent increasing demands for the finer processing to the semiconductor devices, the transfer pattern is sensitive to the aberration of the optical system. Therefore, there is a demand for highly precise measurements of the best focus position and wave front aberration of the projection optical system.
The instant inventor has already proposed one solution method for this problem for imaging a pattern on the reticle with the light irradiated by an illumination optical system, and for measuring a wave front aberration of the projection optical system based on a positional offset between a reference position and a center of the formed image. See, for example, Japanese Patent Application, Publication No. 2003-178968.
Other prior art references include Japanese Patent Applications, Publication Nos. 2003-318090 and 2002-289494, and U.S. Pat. Nos. 5,828,455 and 5,978,085.
Japanese Patent Application, Publication No. 2003-178968 maintains the mask stage and the wafer stage still during the measurement. The instant inventor has discovered that this method is suitable for the stepper but not always suitable for the scanner. There are two types of measurements for the scanner: One maintains these stages still during the measurement, and the other dynamically scans these stages during the measurement. The measurement of the best focus position at the scan state is different from that at the still state in that the measurement at the scan state needs to measure the control performance of the exposure apparatus in the focus direction (or the Z direction) in a real-time basis during scanning. In measuring the aberration of the projection optical system, the mask is scanned with a normal slit illumination (while the wafer is also scanned at the same time), and the entire exposure area on the mask is exposed. The slit has a predetermined width in the scan direction, and the resist image depends upon the integration of rays from an image point range corresponding to the slit width. Unlike the measurement at the still state, the aberration of the projection optical system in the measurement at the scan state should address an integration of the aberrations in the image point range corresponding to the slit width, rather than the aberration for one image point. Therefore, Japanese Patent Application, Publication No. 2003-178968 and other prior art references, which maintain the stages still during the measurement, cannot precisely measure the best focus position and the wave front aberration of the projection optical system with precision.
Accordingly, it is an exemplary object of the present invention to provide a measuring method and apparatus for measuring the optical performance, such as an aberration and the best focus position, of a target optical system more precisely than the prior art, an exposure method and apparatus using the same, and a device manufacturing method.
A method according to one aspect of the present invention for measuring an optical performance of a projection optical system in an exposure apparatus that exposes a pattern on a reticle onto a substrate, includes the steps of determining an pupil area in the projection optical system, scanning a test reticle or a reference plate, imaging a test pattern on the test reticle or the reference plate onto a surface of the substrate via the pupil area in the projection optical system which has been determined by the determining step, and measuring a positional offset between a predetermined position and an image of the test pattern that has been imaged by the imaging step.
A measuring apparatus according to another aspect of the present invention for measuring an optical performance of a target optical system, includes an illumination optical system for illuminating a test pattern that extends in a predetermined direction by using measuring light, a drive unit for scanning the test pattern in the predetermined direction relative to the measuring light; and a measuring unit for measuring a position of an aerial image or an image on a substrate imaged by the target optical system, by introducing, to the target optical system, the measuring light that passed the pattern.
A measuring method according to another aspect of the present invention for measuring an optical performance of a target optical system, includes the steps of obtaining information on a position of an aerial image or an image on a substrate imaged by the target optical system, by scanning a pattern that extends in a predetermined direction with measuring light, and by introducing, to the target optical system, the measuring light that has passed the pattern, and calculating the optical performance of the target optical system from the information obtained by the obtaining step.
An exposure method according to another aspect of the present invention includes the steps of adjusting a projection optical system as a target optical system based on the optical performance that has been calculated by utilizing the above measuring method, and exposing an object by using the projection optical system that has been adjusted by the adjusting step.
An exposure apparatus according to another aspect of the present invention for exposing a pattern on a reticle onto an object in a step and scan manner, includes a projection optical system for projecting the pattern onto the object, and a measuring apparatus according to claim 6 for measuring an optical performance of the projection optical system.
A device manufacturing method according to another aspect of the present invention includes the steps of exposing an object using the above exposure apparatus, and developing the object that has been exposed.
Other objects and further features of the present invention will become readily apparent from the following description of the preferred embodiments with reference to the accompanying drawings.
Referring now to
The test pattern TP uses another pattern or a periodic pattern proposed in Japanese Patent Application No. 2001-264582 by this inventor, which has approximately the same pitch or interval between lines and spaces, and individual space widths that transmit the light reduce from a centerline of the periodic pattern or a pattern of the center space to the outer patterns.
These patterns reduce the diffracted light, and form a light intensity distribution approximately close to the illumination aperture stop 4's shape on a pupil surface 10 a in the projection lens 10. The light intensity distribution of a pattern image formed through the projection lens 10 can be regarded as one large pattern that has less distortion and does not resolve a gap between the lines. As disclosed in Japanese Patent Applications, Publication Nos. 2003-178968 and 2003-318090, the opening shape of the special illumination aperture stop 4 is optimized with a specific Zernike term or the aberration of a real device pattern by means of a database of the Zernike sensitivity to positional offset amounts, which has been previously calculated for each position on a pupil surface of the projection lens 10. In other words, the illumination optical system's effective light source distribution is set and the light that passes the pupil area in the projection optical system is restricted so that the positional offset amount of the test pattern image from a predetermined position depends primarily on one of the coefficients with respect to the specific Zernike term or the real device pattern. In particular, the illumination optical system's effective light source distribution is set and the light that passes the pupil area in the projection optical system is restricted so that the positional offset amount of the test pattern image from a predetermined position have a 1:1 relationship with one of the coefficients with respect to the specific Zernike term or the real device pattern.
This embodiment irradiates the principal ray LP onto the test pattern TP on the reticle 9 via the illumination optical system having an optimized aperture stop shape, and measures the aerial image imaged by the test pattern TP on the reticle 9 or transfers the pattern image TPa on the photosensitive substrate. Next, this embodiment changes a direction of the principal ray by rotating the aperture stop 4 in the illumination optical system or by replacing the aperture stop 4 with a different aperture stop, and measures the aerial image imaged by the test pattern TP on the reticle 9 or transfers the pattern image TPa on the photosensitive substrate. By repeating the above steps, this embodiment measures the specific Zernike coefficient or the aberration of the real device pattern on the pupil surface 10 a on the projection optical system 10.
The above approach is applicable to the measurement of the best focus position. In this case, it is unnecessary to optimize the shape of the illumination optical system's stop 4, and only the oblique incident illumination disclosed in Japanese Patent Application, Publication No. 2002-289494 is enough.
Plural patterns that are the same as the test pattern TP are formed on the reticle 9 near the test pattern TP. One PH is formed on the opposite surface to one TP so that the opening part PH corresponds to the test pattern TP. These PHs correspond to different opening parts or arranged rotationally symmetrically. The pattern images at the same image point for these TPs by slightly shifting a position of the reticle. The best focus position, Zernike coefficient and the real device aberration are measured in the same manner as the above method that is described with reference to
Referring now to
The measurement light supplied from a light source 1 illuminates a reticle 9 via an illumination optical system 2.
The above approach can measure the aberration for each image point when the test patterns 18 a and 18 b are provided at some positions on the same reticle or on the different reticles.
The control accuracy of the focus and tilt of the exposure apparatus during scanning in the scan exposure can be measured in the similar procedure. The usually used illumination optical system's stop is the stops 4 a and 4 b shown in
A description will now be given of an embodiment in which the exposure apparatus adopts the measurement principle shown in
The test pattern is the same pattern in this embodiment. Plural sets of opening parts and test patterns are arranged near the image point to be measured.
When the incident angle of the illumination light supplied from the illumination optical system is smaller than σ of 1.0 and the incident angle of σ of 1.0 or greater is necessary, a chrome pattern that causes diffusions is arranged in the glass surface of the opening part 16 as shown in
An alternative embodiment scan-exposes the same mark 18 a in the above approach. Then, instead of changing the mark size for each opening part, a reference mark 33 that is located at another reticle area and has a different mark size is moved to the wafer stage or the reticle stage and exposed so that the reference mark 33 overlaps the mark 18 a.
An embodiment that measures focus and tilt changes at the time of scanning forms the oblique incident illumination using the opening part 16 on the reticle 9, irradiates the light onto the test pattern 15 through scanning, and measures an offset of the formed image. The image formed by the oblique incident illumination causes a positional offset due to the focus position on the imaging surface. Since a relationship between this positional offset amount and the focus amount approximately accords with the incident angle of the oblique incident illumination, the focus change can be measured if the positional offset of the pattern during the scanning can be detected. The tilt change can also be measured by providing a pattern in the image point direction of the projection lens if the positional offset during the scanning can be detected.
The instant embodiment provides the opening part 31 corresponding to the test pattern 30 on the opposite surface of the test pattern 30 on the reticle 9. The illumination is exposure of a normal illumination condition (large σ) or uses an irradiation through the scope 19. The opening part 31's shape and position on the back surface of the test reticle 9 may receive the oblique incident illumination, and the opening part 31 may be dimensioned so that the illumination incident angle is close to σ=1 and the light intensity matches the scan speed. each set of the test pattern 30 and the opening 31 is arranged in the image-point direction at proper intervals, and the row is arranged also in the scan direction at proper intervals on the reticle 9.
A description will now be given of the arrangement example of the test reticle in the embodiment that includes two opening parts 31 and 32 shown in
A reference mark 33 is located which is different in mark size from the test pattern 30 that is located in the other reticle area. A light shielding part above the reference mark 33 is not particularly necessary. The reference mark 33 does not have to be a special pattern like the test pattern 30, and is a frame mark having a width of 2 μm in this embodiment. If an incident angle of the illumination light supplied from the illumination optical system 2 is smaller than σ=1.0 and a wider illumination incident angle is needed or a flat light intensity distribution is necessary, an optical element, such as a diffuser panel and a CGH, is inserted into the illumination optical system or arranged at the opposite surface of the test pattern. A description will be given of the procedure. The procedure includes the steps of setting the test reticle 30, provides scan-exposure after the illumination condition is driven or set to the predetermined, and transfers the entire pattern on the test reticle 9 onto the photosensitive substrate (wafer) W. In general, the illumination condition in this case is the large σ condition. Next, this embodiment moves the wafer stage 12, and provides the scan exposure again, transfers the test pattern 30 so that the test pattern 30 overlap the reference mark 33. The transferred image is developed, and the positional offset measuring apparatus calculates the positional offset, and converts the positional offset into the focus and tilt amount from the predetermined conversion coefficient.
Another embodiment arranges, as shown in
Alternatively, a CCD camera provided on the wafer stage in the apparatus can photograph the aerial image to measure the center position of the image.
By feeding back the obtained measurement values to the body system, as shown in
The exposure apparatus includes an illumination apparatus (not shown) which is different from or the same as the measuring apparatus, a reticle that has a circuit pattern of semiconductor devices (such as a semiconductor chip, e.g., ICs and LSI, a liquid crystal panel, and a CCD), and a plate, and exposes the circuit pattern on the reticle onto the plate, for example, in the step and scan manner. The inventive exposure apparatus is not limited to the scanner, but it precisely measures and corrects the optical performance in the projection optical system in the scanner.
A description will now be given of an embodiment of a device manufacturing method using the above exposure apparatus.
Thus, the present invention can provide a measuring method and apparatus for measuring the aberration and the best focus position of a target optical system more precisely than the prior art, an exposure method and apparatus using the same, and a device manufacturing method.
Further, the present invention is not limited to these preferred embodiments, and various modifications and changes may be made in the present invention without departing from the spirit and scope thereof. For example, the present invention is applicable, for example, to use of the light-receiving element provided on the wafer stage to measure the light intensity on the wafer stage and the transmittance of the projection optical system.
This application claims foreign priority benefits based on Japanese Patent Application No. 2003-417212, filed on Dec. 15, 2003, which is hereby incorporated by reference herein in its entirety as if fully set forth herein.
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|US5828455||Mar 7, 1997||Oct 27, 1998||Litel Instruments||Apparatus, method of measurement, and method of data analysis for correction of optical system|
|US6633390||Mar 20, 2001||Oct 14, 2003||Canon Kabushiki Kaisha||Focus measurement in projection exposure apparatus|
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|US7190443||Dec 3, 2002||Mar 13, 2007||Canon Kabushiki Kaisha||Reticle and optical characteristic measuring method|
|US20020015158 *||Mar 20, 2001||Feb 7, 2002||Yoshihiro Shiode||Focus measurement in projection exposure apparatus|
|US20020159040 *||Feb 12, 2002||Oct 31, 2002||Nikon Corporation||Specification determining method, projection optical system making method and adjusting method, exposure apparatus and making method thereof, and computer system|
|US20030091913 *||Oct 1, 2002||May 15, 2003||Canon Kabushiki Kaisha||Aberration measuring method and projection exposure apparatus|
|US20030133099 *||Dec 3, 2002||Jul 17, 2003||Canon Kabushiki Kaisha||Reticle and optical characteristic measuring method|
|US20040109148 *||Dec 2, 2003||Jun 10, 2004||Canon Kabushiki Kaisha||Exposure apparatus|
|JP2001264582A||Title not available|
|JP2002289494A||Title not available|
|JP2003178968A||Title not available|
|JP2003318090A||Title not available|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US8248580||Apr 30, 2009||Aug 21, 2012||Canon Kabushiki Kaisha||Scanning exposure apparatus and method of manufacturing device|
|U.S. Classification||355/52, 355/77, 355/53|
|International Classification||G01M11/02, G03B27/68, G03B27/42, H01L21/027, G03F7/20, G03B27/32|
|Dec 15, 2004||AS||Assignment|
Owner name: CANON KABUSHIKI KAISHA, JAPAN
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:SHIODE, YOSHINORI;REEL/FRAME:016100/0061
Effective date: 20041207
|Jun 24, 2005||AS||Assignment|
Owner name: CANON KABUSHIKI KAISHA, JAPAN
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:SHIODE, YOSHIHIRO;REEL/FRAME:016715/0461
Effective date: 20041207
|Jul 25, 2012||FPAY||Fee payment|
Year of fee payment: 4